University of Illinois Extension

Illini PoultryNet Papers

Molting, Bird Density, and Animal Welfare
Ken W. Koelkebeck


In today's commercial poultry industry, technological advances in management practices and housing systems has made this industry very efficient. These improved practices have benefitted the consumer by keeping prices for poultry meat and eggs at a stable and low level. However, over the past 35 to 40 years some questions and concerns have been raised by the general public regarding the intensive raising of poultry in today's commercial systems.

Today's commercial poultry producer uses performance measures to determine the profitability and welfare (well-being) of a flock. The assessment of the well-being or welfare of a poultry flock is judged differently by some people associated with the animal welfare movement. These people essentially believe that some of the current methods of raising and housing poultry do not support their well-being and welfare. They believe that all poultry should not be caged, penned in large groups, induced molted, fed antibiotics, or subjected to other current poultry industry practices. Induced molting and bird/cage density have been two practices that have drawn considerable attention by researchers in the field of poultry well-being and welfare. Thus, this paper focuses on research conducted in induced molting techniques and bird density/cage housing systems and relates this research to poultry well-being and welfare.


Concern for the welfare of the hen during the molt has been expressed by animal activists groups, poultry scientists, and commercial poultrymen in recent years. In a recent review article presented at the First North American Symposium on Poultry Welfare, Ruszler (1998), presented an excellent review of the health and husbandry considerations of induced molting. In that article, he discussed the positive and negative aspects of molting programs and related them to the concerns about poultry well-being during an induced molt. He mentioned that early work by Mrosovsky and Sherry (1980) showed that a hen which is undergoing a natural molt will reject feed for an extended period of time. In addition, he commented that a broody hen (chicken or turkey) will naturally go for 21 or 28 days consuming little or no feed.

There are several types of induced molting methods employed in today's commercial egg industry. Most of these programs involve the use of feed withdrawal (fasting) to produce a cessation of egg production. Guidelines regarding the specifics of molting programs have been published by several institutions (Swanson and Bell, 1974; Brake and Carey, 1983; Ruszler, 1996). These programs recommend using fasting periods of varying lengths. For example, Brake and Carey (1983) recommended fasting a flock until they reached a target body weight loss. The length of fast in this program is usually at least 10 days or more. Other molting programs that have involved the use of a short feed withdrawal period (4 to 5 days) have showed that egg performance results can be comparable to those achieved by a traditional feed removal program (Koelkebeck et al., 1992; Ruszler, 1996). Kuney and Bell (1989), however, reported that hens that were fasted for 4 days returned to production sooner than those fasted for 10 or 14 days, but postfast egg production (36 wk) was lower for hens fasted for only 4 days. Thus, the research conducted on the use of a short feed withdrawal period are contradictory.

In a study at the University of Illinois (Koelkebeck et al., 1992), two experiments were conducted to determine the effects of varying length of feed withdrawal on postmolt laying hen performance. It was of interest to see if comparable performance results could be achieved by fasting hens for only 4 days compared to 7, 10, or 14 days. In Experiment 1, commercial laying hens at 65 wk of age were continuously fed, fasted for 4 or 10 days. The hens fasted for 4 days were fed a layer ration immediately after the fast and the ones fasted for 10 days were fed a 16% protein molt ration after the fast until the hens were laying at a 10% rate of production, then fed a 16% protein laying ration. Production performance was monitored for 35 wk thereafter. In Experiment 2, two extra treatments were added and they consisted of fasting hens for 7 and 14 days.

In this study, only two birds died during the fasting periods in Experiment 1 and both occurred in the 10-day fasted treatment. Total mortality was 13.1, 7.1, and 8.3% for the fed, 4- and 10-day fasted groups, respectively. Similar mortality results occurred in Experiment 2. Body weight loss for the 4- or 10-day fasted groups in Experiment 1 were 20 and 29%, respectively; while body weight losses of 18, 24, and 34% occurred for hens fasted for 4, 7, or 14 days, respectively, in Experiment 2. The results for egg production and egg specific gravity are depicted in Tables 1 and 2. For egg production, no differences were found between treatments in both experiments when Weeks 5 to 35 were compared, however, hens fasted for 14 days produced less eggs than those continuously fed in Experiment 2 when the Weeks 1 to 35 were compared. For egg specific gravity, the hens given the longer fasting period generally had better shell quality than those not fasted. Thus, this study documented that egg production in particular is just as good for hens fasted for only 4 days compared to 7, 10, or 14 days. However, this study also showed that egg shell quality was poorer when hens were fasted for a short period compared to the conventional time period (10 to 14 days) (Table 2).

In a more recent study, Minear (1998) compared performance results from hens fasted for various lengths and fed different diets. In one study, hens were subjected to the following treatments: 1) hens fasted for 6 days followed by the feeding of a molt ration every other day for 18 days then feed restricted on a daily basis, 2) hens fasted for 4 days then fed oats free choice, 3) hens fasted for 4 days then fed a 10% protein molt diet, or 4) hens fasted for 8 days then fed a 14% protein molt diet. All hens were light stimulated at 35 days from the start of feed withdrawal and they were all fed a layer diet at 42 days following the initiation of fasting.

Table 3 shows the results for mortality and layer performance from 6 to 10 and 6 to 30 weeks from the start of the molt. Mortality did not differ significantly between the treatments. The best early egg production occurred with Treatment 3, but hens in this treatment had the lowest feed conversion. In addition, there were no significant effects on egg weights or on case weights (avg. 50 pounds during lay period). Table 4 shows that the hens on the soft molt (Treatment 1) had the lowest feed cost per dozen eggs. Thus, this study indicated that hens subjected to a short fasting period will produce adequately during the lay cycle.

Thus, the studies cited previously indicate for the most part that satisfactory performance can be achieved from a molting program in which a short time period for feed withdrawal is used. These results can be achieved without compromising the birds health due to inducing a molt by feed withdrawal. However, in order to provide more information about the health and welfare concerns of feed withdrawal to induce molting, other factors should be examined in addition to performance results. To provide more information in this area, a recent study by Webster (2000) examined the behavioral responses of laying hens following the withdrawal of feed. In this study, commercial hens were induced molted by feed withdrawal until 35% of their initial body weight was lost. The behavior of 36 molted and 36 control hens were video recorded on days 1 to 3, 8 to 10, and 19 to 21 of the feed withdrawal period when the hens reached 15, 25, and 35% body weight loss. The hens that had feed withdrawn were fed a pullet grower until Day 28 of the feed withdrawal period, then fed a layer ration.

The results of this study showed that second cycle egg production averaged 15.5 eggs per hen housed to 40-wk postmolt initiation. In addition, hens that had feed withdrawn had significantly lower mortality (2 vs 12%) than control hens. The fasted hens showed increased aggression on the first day of the feed withdrawal period, then exhibited increased standing, head movement, and nonnutritive pecking on Day 2. Table 5 shows the comparison between hens fasted and control fed for the 1 to 3, 8 to 10, and 19 to 21 days of the feed withdrawal period. Basically, these results showed that fasted hens spent less time at the feed trough and more time pecking at the cage and feather pecking than control hens. In addition, fasted hens seemed to rest more than control hens. This study also showed that hens that had feed withdrawn still showed behaviors that were consistent with alertness.

In summary, the work presented here indicates that for the most part, today's commercial molting practices are not harmful on the hen and in fact, maybe beneficial towards her overall health. More and more commercial layer companies are moving towards utilizing a molting program that uses a short feed withdrawal period and achieving good success. Finally, in a recent article, Garlich (1995) stated that the use of feed withdrawal to initiate a molt is "within the normal physiological capability of a hen."


Another management practice used in the commercial poultry industry that has received considerable attention from the animal rights community is the practice of housing layers and other poultry in intensive housing situations. Concerns have been voiced on cage housing in and of itself, bird density and number of birds housed per cage, in addition to the floor space allowance given to birds housed in large confinement buildings. Some of the research in this area has attempted to compare intensive cage production systems with those such as floor pens, aviaries, and get-away cages. This research has focused on production and well-being factors as the basis of comparison. In addition, the bulk of the research conducted in this area has focused on the effects of cage population and density allotted per bird in cages. It has been shown that crowding and high-density situations can have negative effects on production and well-being (welfare) of birds themselves. So, the question still remains as to what should the appropriate cage density be. In the European community strict regulations regarding cage density has been adopted for laying hen operations (Blokhuis, 1999). A summary of these regulations is depicted in Table 6. This table shows that the space allotted per bird is considerably more than typical cage situations here in the U.S. commercial industry (48 to 60 sq. in. per bird). The reduced cage floor area provided for hens here in the U.S. does not mean that the birds health and well-being is compromised, however.

Most of the early literature published in this area has shown that reduced performance will occur if cage stocking density is increased. Adams and Craig (1985) summarized research conducted from 1971 to 1983 and they found that reducing cage floor space from 60 in2 to 48 in2/hen reduced eggs per hen housed by 16, reduced feed consumption 1.0 g/hen/day, and increased mortality by 4.8%. In a study conducted after this review article was published, an analysis of 23 different production variables was conducted with laying hens (Koelkebeck et al., 1987). In this study, production, physiology, and behavior parameters were measured for laying hens maintained in deep and shallow cages at two densities and three cage populations. Tables 7 and 8 depict the results. It is interesting to note that improved livability was noted for hens given 54 vs 72 in2/hen. In addition, production differences were not seen between the space allotted per hen and cage population size. More recently, production performance results affected by space allowance per hen was reported by Anderson (2000). The results of the 33rd North Carolina Layer Performance and Management Test reported that egg production was reduced for hens given 48 vs 64 sq. in. per bird (Table 9).

More recent work done in the area of space allocation for layers and the effect of bird density on performance and laying hen well-being (welfare) has ben the work on the Edinburgh Modified Cage (Appleby, 1998). In this research, a modified laying cage was developed for use in European laying hen facilities in response to public and legal pressure for improvement of laying hen welfare. In this study, a cage was designed that had a perch, nest box, and dust bath (Figures 1 and 2). The results showed that the physical condition of the birds were improved compared to control birds in conventional cages. However, because of the increased space needed for the perch, nest box, and dust bath, egg production costs were more than in conventional cages.

In summary, bird density allocation for laying hens and growing birds is an important consideration for the commercial poultry industry. If animal welfare concerns demand that more space be given to poultry in intensive management systems or cages for laying hens be abolished, then production costs associated with these changes would be dramatically increased.


Adams, A.W., and J.V. Craig, 1985. Effect of crowding and cage shape on productivity and profitability of caged layers. A survey. Poultry Sci. 64:238-242.

Anderson, K.E., 2000. Results of the 33rd North Carolina Layer Performance and Management Test. North Carolina State University. February 16, 2000.

Appleby, M.C., 1998. The Edinburgh modified cage: Effects of group size and space allowance on brown laying hens. J. Appl. Poultry Res. 7:152-161.

Blokhuis, H.F., 1999. European regulations for laying hens. Presented at European Symposium on Quality of Eggs and Egg Products. Bologna, Italy.

Brake, J.T., and J.B. Carey, 1983. Induced molting of commercial layers. North Carolina Agricultural Extension Service Poultry Science and Technical Guide No. 10. North Carolina Agricultural Extension Service, Raleigh, NC.

Garlich, J.D., 1995. Study: Hens are unaffected by fasting during forced molt. Poultry Times, Feb. 27:13.

Koelkebeck, K.W., M.S. Amoss, Jr., and J.R. Cain, 1987. Production, physiological, and behavioral responses of laying hens in different management environments. Poultry Sci. 66:397-407.

Koelkebeck, K.W., C.M. Parsons, R.W. Leeper, and J. Moshtaghian, 1992. Effect of duration of fasting on postmolt laying hen performance. Poultry Sci. 71:434-439.

Kuney, D.R., and D.D. Bell, 1989. Effect of molt duration on performance. In: Proceedings of the University of California Poultry Symposium, University of California, Riverside, CA.

Minear, L.R., 1998. Molting hens the lite way. Presented at 1998 Multi-State Poultry Feeding and Nutrition Conference, Indianapolis, IN.

Mrosovsky, N., and D.F. Sherry, 1980. Animal anorexias. Science 207:837-842.

Ruszler, P.L., 1996. The keys to successful force molting. Virginia Cooperative Extension Service, Publication 408-026 (revised), Blacksburg, VA.

Ruszler, P.L, 1998. Health and husbandry considerations of induced molting. Poultry Sci. 77:1789-1793.

Swanson, M.H., and D.D. Bell, 1974. Force molting of chickens. II. Methods. University of California Leaflet 2650. University of California, Davis, CA.

Webster, A.B., 2000. Behavior of White Leghorn laying hens after withdrawal of feed. Poultry Sci. 79:192-200.

TABLE 1. Duration of fasting and egg production

  Hen-day egg production
  1-35 wk 5-35 wk
Treatment Exp. 1 Exp. 2 Exp. 1 Exp. 2
  -- (%) --
Fed, controls 64 68a 64b 69
4-d fast 67 67ab 73a 72
7-d fast - 67ab - 74
10-d fast 67 - 75a -
14-d fast - 73b - 72

a,b = P < .05

Adapted from Koelkebeck et al. (1992)

TABLE 2. Duration of fasting and egg specific gravity

  Exp. 1 Exp. 2
Treatment 16-19 wk 32-35 wk 16-19 wk 32-35 wk
  -- (g/cm3) --
Fed, controls 1.076c 1.074b 1.077c 1.073b
4-d fast 1.079b 1.076ab 1.079b 1.075b
7-d fast --- --- 1.080b 1.074b
10-d fast 1.081a 1.078a --- ---
14-d fast --- --- 1.083a 1.078a

a,b = P < .05

Adapted from Koelkebeck et al. (1992)

TABLE 3. Mortality and layer performance

    Performance (6-10 wk) Performance (6-30 wk)
Treatment Total Livability H-D Egg Prod. Feed Intake Feed Conv. H-D Egg Prod. Feed Intake Feed Conv.
  (%) (%) (lb/100/d) (lb/doz.) (%) (lb/100/d) (lb/doz.)
1 (6-d fast-molt) 99.36 45c 20.7b 5.6ab 77 22.5y 3.7a
2 (4-d fast-oats) 98.36 43c 20.8ab 5.8a 76 22.6y 3.7a
3 (4-d fast-10% P) 98.45 52a 20.4b 4.7c 78 22.8xy 3.6b
4 (8-d fast-14% P) 98.11 47b 21.1a 5.4a 78 23.0x 3.7a

Adapted from Minear (1998)
a,b = P < .01
x,y = P < .10

TABLE 4. Economics of molt programs for 30 weeks postmolt

    Feed Feed Cost
Treatment Eggs Molt Lay Molt Lay Total
  (doz.) -- (lb/hen) -- -- (cents/doz.) --
1 (6-d fast-molt) 10.63 4.0 37.9 3.0 28.5 31.5
2 (4-d fast-oats) 10.65 3.9 37.9 3.6 28.8 32.3
3 (4-d fast-10% P) 10.73 5.6 38.3 3.9 28.5 32.3
4 (8-d fast-14% P) 10.70 4.5 38.7 3.3 28.9 32.2
Adapted from Minear (1998)

TABLE 5. Behavior of hens not fasted vs fasted

  Day 1-3 Day 8-10 Day 19-21
Behavior Activity Control Fasted Control Fasted Control Fasted
  -- (% observations) --
Head Movement 32 43 28 29 26 26
Feeder 30 5 34 2 40 1
Non-nutritive Pecking 2 5 2 7 2 8
Resting 4 6 5 23 6 40
Adapted from Webster (2000)